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Alfalfa leafcutting bees

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Megachile rotundata

Alfalfa leafcutter bee (Megachile rotonda)

Photo: Penn State

Alfalfa leafcutter bee (Megachile rotonda)

Photo: Peggy Greb

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Description

They are smaller than our indigenous leafcutting bees (5 to 9 mm long, rather than 9 to 20 mm). They are stocky, with broad heads, and females have a ventral brush of short, stiff silver-grey hairs under the abdomen.

Life cycle

Adult leafcutting bees overwinter in individual cells. Mating occurs as soon as the females emerge, after the males.

The females build their own nests and stock them with food. They may make a nest in various kinds of cavities, make a hole in the ground or use a manmade nest.

They make eight to twelve cells per nest, depending on the length of the cavity. The cells, laid end to end, are made with bits of leaves or petals cut up by the bee. When a cell is ready, the bee stocks it with pollen and nectar and lays an egg in it. Once the nest is full, the bee blocks off its entrance. A female may build more than one nest.

Larvae are white when they hatch. Each one has enough food in its cell for its full development. They overwinter in this shelter, in what is called a “prepupal” stage (the final larval development stage). When warmer weather returns, the insect turns into a pupa and then an adult.

Where are they from?

This species was accidentally introduced into North America from Europe. It was caught for the first time in the United States in 1937.

Geographic distribution

Megachile rotundata is a naturalized species that is very well established in Quebec. It is found throughout the province since it is used with various crops.

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Habitat

These leafcutting bees live on farmland but also in urban environments, and even downtown. They can live in environments modified by humans (landfill sites or roadsides).

Diet

Larvae feed on pollen and nectar.

Did you know?

Interesting facts

Alfalfa leafcutting bees are raised commercially on a large scale. They are used in many countries to pollinate alfalfa, a plant with purple flowers grown for its seeds or as fodder. Canada is the world’s largest producer and exporter of Megachile rotundata cocoons.

These bees readily nest in easy-to-dismantle nesting boxes set up for them. Most often these consist of a series of corrugated polystyrene panels, forming tunnels where the females can build their nests. This beekeeping system makes it easy to remove the cocoons in the fall.

A female takes about 2.5 hours to make a cell, under suitable conditions, and then about five hours to stock it with food. This means that it takes a total of 7.5 hours per cell on average, and a bee generally makes just one a day.

Ecological roles

These bees are important pollinators in the wild and on farms and in urban environments. They are also a source of food for many animals.